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From: rick@cadtec.UUCP (Rick Auricchio)
Newsgroups: net.micro
Subject: Re: Reading Apple II disks
Message-ID: <75@cadtec.UUCP>
Date: Wed, 10-Apr-85 13:20:06 EST
Article-I.D.: cadtec.75
Posted: Wed Apr 10 13:20:06 1985
Date-Received: Mon, 15-Apr-85 03:25:20 EST
References: <1535@decwrl.UUCP>
Reply-To: rick@cadtec.UUCP (Rick Auricchio)
Distribution: net
Organization: Cadtec Corp., San Jose CA
Lines: 32

lds ~110Kb by using the 5/8 GCR encoding.

Sixteen-sector format, however, "stretched" the rules a bit.  It allows a flux
change every 4, 8, or 12uSec.  Though the laws of FM say you must not do that,
Woz did (and modified the state machine a bit).  Now we get more GCR codewords
allowable (~64).  [All the valid 10/13 sector ones plus new ones with two
consecutive zero bits].  Using a 6/8 GCR gives ~140Kb capacity.

Only about 10 engineers at Apple know/knew the real details of the disk
and how to write "core" routines to read/write/format etc.  At least three of
us are no longer there, having been gone since the days of the Apple ///. 

Matter of fact, I wrote the floppy driver/formatter for the ///. The disk ///
is *identical* to the disk ][, except for the disk-switch sensing which occurs
when the wrote-protect switch toggles (try removing a disk on either drive;
hear the wp switch click).  Extra chips on the disk analog card latch-up the
read-data line (software detects the lockup) and free it on a seek.  It is
possible, though I've forgotten how, to take a disk /// and hotwire it to run
on the ][/ or //e.
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